Luminous discharge tube



Feb. 23, 1937.

M. PENNYBACKER 2,071,426

LUMINOUS DI SCHARGE TUBE Filed Dec. 20, 1934' WITNESS Invm T n R MILESPENHYBACKER BY I WM 5 MM ATTORNEYS Patented Feb. 23, 1937 PATENT OFFICELUMINOUS DISCHARGE TUBE Miles Pennybacker, West Orange, N. J., assignorto Voltarc Tubes, Inc., Newark, N. J., a corporation of New JerseyApplication December 20, 1934, Serial No. 758,398

6 Claims.

This invention relates to new and useful improvements in luminousdischarge tubes, and is in large part a division of my co-pendingapplication Serial No. 592,931, filed February 15, 1932.

The main object of this invention is to provide a luminous dischargetube having unidirectional current conductivity.

A further object of the invention is to provide a luminous dischargetube, the anode of which is suiliciently restricted in area to impartunidirectional current conductivity to the tube.

Still another object of the invention is to provide a luminous dischargetube having unidirectional current conductivity and which is capable ofwithstanding high reverse voltages, and, more specifically, to providean anode that is capable of withstanding the high voltage necessary tocause current conduction in a long luminous tube without permittingsubstantial reverse current to flow when the voltage is reversed.

Other objects and advantages of the invention relate to details of theelectrode structures and their arrangement within the tube, and willappear more fully from the following description taken in connectionwith the accompanying drawing, in which:

Figure 1 is a circuit diagram illustrating a luminous discharge tubesystem in which a plurality of tubes constructed in accordance with myinvention are connected for'operation from a single source ofalternating current;

Figure 2 is a view of a luminous discharge tube having substantially,unidirectional conductivity adapted for use in a system such as shown inFigure 1;

Figure 3 is an enlarged sectional view of the cathode electrode of thetube shown in Figure 2;

Figure 4 is an enlarged sectional view of the anode electrode of thetube shown in Figure 2; and

Figure 5 is an enlarged sectional view of a modified form of anodeconstruction adapted to be used in a tube of the form shown in Figure 2.

The resistance of luminous discharge tubes decreases rapidly as thedischarge begins. As a result, it has heretofore not been practical tooperate luminous discharge tubes in parallel from a single source ofcurrent except by the use of ballasting reactors, or resistances inseries with each tube. Without such reactance or resistance, one tubewill discharge before the others and thereupon the resistance of thedischarging tube will decrease to such an extent that the other tubeswill not discharge. Because of this fact, luminous discharge tubes whichare to be energized from a single source of current commonly areconnected in series, thereby necessitating the use of higher voltagesthan would be necessary if the tubes could be operated in parallel.

The tube of my invention overcomes this difficulty and permits theoperation of two parallel branch circuits from a single source ofcurrent without employing separate external reactance or resistance inseries with each tube or parallel branch. Each parallel branch mayinclude two or more tubes in series as schematically illustrated inFigure 1.

The tubes III, II, I3 and I4 of Figure 1 have a unidirectionalconductivity. The tubes I0 and II are connected in series, anode tocathode, to form a branch I2 which offers a relatively low resistance tothe flow of current in the direction indicated by the arrow and arelatively high resistance to the flow of current in the oppositedirection. The parallel branch I5 consists of tubes I3 and II connectedcathode to anode, and offers a relatively low resistance to the flow ofcurrent in the direction of the arrow and a relatively high resistanceto the iiow of current in the 0pposite direction.

The two parallel branches I2 and I5 are connected across the alternatingcurrent mains I6 and H which, in turn, are connected to a suitablesource of current as a high reactance transformer I8. Such highreactance transformers are commonly used in this art, and, as is wellknown, they serve to limit the current flowing through the loadconnected thereto. It is, therefore, apparent that as alternatingcurrent voltage is applied across the mains I6 and H, the branch I2 willdischarge only when the voltage is applied in one direction and thetubes in branch I5 will discharge only when the voltage is of oppositepolarity.

In the system as shown in Figure 1, all of the tubes will dischargeunidirectionally, but neither branch is required to withstand themaximum reverse voltage of the current supply mains because the lowerresistance branch will discharge before the voltage wave reaches amaximum value. It is, therefore, apparent that the tubes in this systemare more free from failure due to insulation breakdown, than tubessubjected continuously to a high voltage, as is necessarily encounteredin a. single series connected system ofunidirectional tubes.

It is also apparent that tubes operating unidirectionally in the mannerabove described will have a longer life than when operatedbi-directionally since, in the case of the former, each parallel branchdischarges only during altemate half cycles, whereas in tubes havingbi-directional conductivity, each tube discharges on both half cycles.If GO-cycle current is used, the intermit- 5 I tent operation of therespective branches is not apparent to the eye, and, due also toretention of vision, the brilliancy of the tubes is apparently exactlythe same as for continuous operation of the same tube on alternatingcurrent.

I have found that the brilliancy can be increased by increasing thecurrent density either by reducing the tube diameter for the samecurrent or by increasing the current with the same diameter. By thismeans a greater apparent brilliancy may be obtained with each tube withless power consumption per unit of tube than is obtained in the ordinarybi-directional operation and with greater total footage per tube on thesame applied voltage. Consequently, by using the tube of my invention inthe above-described manner, the length of luminous tubes operated from asingle source of current supply may be greatly increased with anapparent increase in light output for the same power input.

It is, however, necessary to provide for the contingency that ariseswhen one tube becomes inoperative, or when one of the two parallelbranches becomes an open circuit from any other cause. If the remainingbranch isto remain unidirectional, it must now withstand practically thefull open circuit voltage of the transformer on alternate half cycles.This means that the anode must be capable of preventing substantialcurrent flow even though the voltage is high enough.

' to initiate a discharge, and the resistance of the remainder of thetube has been correspondingly lowered. In commercial neon signinstallations, where 15,000 volt transformers are customarily employed,the total reverse voltage on the operating branch, in the case of anopen circuit in the other branch, may approach the open circuit voltageof such a transformer. If there are seven tubes in series in theoperating branch, the voltage drop at each of the seven anodes may be ofthe order of 1000 volts.

Anodes of prior art unidirectional tubes would pass a heavy current andbe rapidly destroyed at any such voltages, and prior art unidirectionaltubes have, therefore, been restricted in their commercial use tooperation on low voltages. Even with unidirectional hot cathode tubesoperating in the circuit herein described on 250 to 1000 milliamperes atvoltages as low as 1200 volts, it is sometimes necessary for the anodeitself to withstand more than 400 volts reverse voltage.

The necessity heretofore of employing low operating voltages withunidirectional tubes seriously handicaps their use in advertising anddisplay work, because only short sections of tubing are possible. On theother hand, long sections of tubing are desirable, partly because of thefacility with which they may be bent into pleasing designs, and partlybecause of their increased life and saving in cost of terminals.

For a more complete description of my improved luminous discharge tube,reference will be made to Figures 2, 3, 4 and 5.

In Figure 2, the sealed tube l8 has enlarged ends in which are a cathode20 and an anode 2| separated-by a column of rarefied atmosphere of neon,helium or others of the noble gases. Ordinarily, such a tube may have alength of from five to ten feet and may-be formed into suitable lettersor figures. Electrical connection may be made to the electrodes 20 and2| y 111 8 5 0! terminals 22 and 23 passing through and sealed inexternally extending press structures 24 and 25. A cylindrical shield 26of insulating material such as mica may be employed around the cathode20 on the interior of the tube.

The tube illustrated in Figure 2 has a substantially unidirectionalconductivity by reason of the fact that at the range of gas pressuresnormally used, from ,5 to 25 millimeters of mercury, and within thenormal operating current range of from 15 to 60 milliamperes, thecathode has a relatively low cathode drop by reason of its large areaand the anode has a relatively high cathode drop by reason of its smallarea. For example, in such a tube containing one or more of the noblegases at a given pressure, the exposed area of the anode desirably isless than the area required for normal cathode drop in the same gas andat the same pressure at an instantaneous current of 1.6 milliamperes,and the area of the cold cathode is desirably more than thirty times asgreat.

If it is assumed that the relatively small area required to maintain alow anode drop is available at the anode, it may be said that, ingeneral, the lower the drop at the cathode during discharge and thehigher the drop at the anode during reverse voltage, the stronger theunidirectional tendency, the more stable the operation of the tube andthe greater the unbalance of relative lengths of tube permitted in twoparallel branches.

I have found that a good working. rule to follow to insure thisdifference in drop between the anode and the conventional designs ofcathode is to have the exposed area of the anode such that its normalcurrent density if used as a cathode would be exceeded when current inthe reverse direction is less than 2% of the normal discharge peakcurrent. In practice, I have used an area less than .01 squaredecimeters per ampere of normal discharge peak current.

The cathode electrode 20, as more clearly shown in Figure 3, comprises aconical metal member having its open end toward the column of gascontained in the tube, and its apex connected as by welding to theterminal 22. Conveniently, the conical electrode may be nickel or ironand its inner surface may be treated to reduce the cathode fall ofpotential. By using a conical electrode of narrow angle, the mosteflicient electrode diameter is assured for all reasonable variations ofgas pressure within the tube.

The anode electrode 2|, as shown in Figure 4, comprises a wire 21 whichmay be tungsten, tantalum or nickel connected as by welding to terminal23. An insulating tube 28 preferably of glass is sealed to press 25 andsurrounds anode wire 21 throughout the greater portion of its lengthleaving the end portion of the wire exposed. The anode wire 21 ispreferably further insulated as by means of an outer tube 29 of lava orisolantite which telescopes over the end of the glass tube 28 and leavesonly the end surface of the wire 21 exposed. The joint between the endof tube 29 and the glass tube 28 may be sealed with porcelain cement asshown at 30 for preventing discharge to the anode lead wire at highvoltage.

' A slightly modified anode arrangement is shown in Figure 5. The anodeproper consists of a wire 3| connected as by welding to a lead-inconnection 32 sealed into an external press 33 of tube 34. An insulatingsheath 35 preferably of glass is fused about anode wire 3| prior toplacing it into the tube 34. The anode 3| with its glass sheath 35 maythen be inserted within a glass tube 36. Further insulation is providedby means of a closely fitting sleeve or tube 31 of high temperatureinsulation such as lava or isolantite which is closed at one end withthe exception of a small bore through which the end of anode wire 3|protrudes slightly. Insulating tube 36 may be sealed with a dischargetight joint to the tube 31 by means of porcelain cement applied at thejoint at the end of tube 31 as shown at 38. Thus, upon the subsequentsealing of the lead-in connection 32 and the glass tube 36 into thepress 33, the anode 3| is insulated to the extent that it will limit thereverse current to such a small value as to permit the operation of thetube on an open circuit reverse voltage for several days without harmfuleffects. This condition may arise when one branch of the parallel systembecomes de fective, or, for some other reason, the branch circuit isbroken, which consequently subjects the tubes in the other branch tomaximum reverse voltage.

I have found that if the internal current discharge bombardment processis used in freeing the electrodes within the tube of occluded gases, itis desirable to provide an auxiliary electrode for carrying the heavybombarding current, due to the small area of the anode 3|. This isaccomplished in the structure shown in Figure 5 by providing theauxiliary electrode 39 of some suit able metal. The electrode 39 ispreferably of frusto-conical shape having its small end incircumferential engagement with the tube 31, and its larger endextending beyond the anode wire 3| toward the column of gas containedwithin the tube. A cylindrical shield 40 of insulating material, such asmica, may be employed around the auxiliary electrode 39 on the interiorof the tube.

Electrical connection to the auxiliary electrode 39 is made by means ofa lead-in conductor 4| sealed into the press 33. Thus, during theprocess of evacuating the tube the heavy bombarding current is carriedby the auxiliary electrode 39 and cathode 20, each of which has an areasufiicient for this purpose. When the tube is processed and filled withgas ready for use, leadin connection 4| is clipped off flush with thepress 33. An insulating tube 42 is sealed to press 33 in surroundingspaced relation with the anode lead-in connection 32 to lengthen the airgap between connection 4| and connection 32 so that the same willwithstand high voltage without arcover even under adverse condition ofoperation. It is apparent that if arc-over is permitted to occur, theunidirectional conductivity of the tube is impaired.

The term luminous discharge tube" as used herein is intended to includetransparent or translucent tubes, bulbs and receptacles of variousshapes and materials which are adapted to pass a luminous positivecolumn electric discharge through an atmosphere of gas or gases. Theterm discharge is used to describe the main body of the luminousdischarge, and not the small or transient discharge which may occur withthe relatively small current which may flow in the reverse direction tothe main current in each branch when the tubes are connected in parallelbranch relationship. The term high voltage is used herein to designatealternating voltages in excess of the usual commercial service voltagesof 110, 220 and 550 volts.

By "anode" is meant that electrode of a luminous dischargetube whichreadily permits a substantial flow of electric current when saidelectrode is of a positive polarity and which resists the flow ofcurrent when it is of negative polarity. By "cathode is meant the otheropposing electrode of a luminous discharge tube which contains an anodeand which will readily permit the desired amount of current to flow whenit is of negative polarity. A cathode for a luminous discharge tube maybe characterized as an electrode which will usually conduct currentreadily regardless of its polarity,

The term normal cathode drop is used herein to designate the loss ofpotential on a cold cathode when the current is not suiiicient to causea glow over the entire exposed surface. The cathode drop remains normalas the current is increased to the point where the glow covers theentire exposed surface. If the current is increased beyond this pointthe cathode drop becomes abnormal.

Although I have shown and described a specific tube structure, it is tobe understood that the same is for the purpose of illustration, and manychanges and modifications may be made by those skilled in the artwithout departing from the spirit or scope of the appended claims.

I claim:

1. In a luminous discharge tube, an elongated envelope, an outwardlyextending press at one end of said envelope, a lead-in conductor sealedin said press, a Wire anode connected to said conductor, an insulatingtube surrounding said anode in part and having one end thereof sealed tosaid press, the exposed portion of said anode being restricted to anarea so small as to permit the flow of substantial current in only onedirection, an auxiliary tubular electrode carried by and surroundingsaid insulating tube, a second lead-in conductor sealed in said pressand connected to said auxiliary electrode, said auxiliary electrodebeing adapted to 'arry bombarding current to liberate occluded gasesduring the manufacture of the tube, and an exterior tubular extensionsealed to said press in surrounding spaced relation to said first-namedlead-in conductor for increasing the insulation between said lead-inconductors.

2. A luminous discharge tube comprising an elongated envelope, anoutwardly extending press at one end of said envelope, a lead-inconductor sealed in said press, a conical cathode connected to saidlead-in conductor, a second outwardly extending press at the other endof said envelope, a second lead-in conductor sealed in said last namedpress, a wire anode connected to said last-named conductor, aninsulating tube surrounding said anode in part and having one endthereof sealed to said last-named press, a second insulating tubesurrounding said first-named tube adapted to seal the open end thereofand being provided with an aperture through which the effective area ofsaid anode protrudes, said effective area being so small as to permitthe flow of substantial current in only one direction, an auxiliarytubular electrode carried by and surrounding said last-named insulatingtube, a third lead-in conductor sealed in said second-named press andconnected to said auxiliary electrode, said auxiliary electrode beingadapted to carry bombarding current to liberate occluded gases duringthe manufacture of the tube, and an exterior tubular extension sealed tosaid lastnamed press in surrounding spaced relation to said second-namedlead-in conductor for increasing the insulation between said twolastnamed conductors.

3. In a positive column luminous discharge, tube, an elongated glassenvelope, a pair of electrodes within said envelope, at least one ofsaid electrodes comprising a cone closed at its small end and with itslarge end open to and directed toward the positive column so that thedischarge takes place on the inside surface of the cone, whereby thedischarge is permitted to select the optimum electrode diameter for widevariations of gas pressure within the tube.

4. In a high voltage unidirectional luminous discharge tube, anelongated glass envelope, lead-in conductor sealed in one end of said envelope with a vacuum-tight seal, an open-ended conical electrodeconnected to the said condoctor, a second lead in conductor sealed inthe other end of said envelope with a vacuiun-tight seal, and a secondelectrode in said tube adapted to permit substantial current to flowonly in one direction, whereby said conical electrode is made tofunction as a cathode during the flow of said current, said conicalelectrode being arranged so that the discharge takes place on the insidesurface of the cone, whereby the discharge is permitted to select theoptimum electrode diameter for ordinary variations of gas pressurewithin the tube.

5. In a high voltage unidirectional luminous discharge tube, anelongated glass envelope, a lead-in conductor sealed in one end of saiden" velope with a vacuum-tight seal, an open-ended conical electrodeconnected to the said con ductor, a second lead-in conductor sealed inthe other end of said envelope with a vacuum-tight seal, a secondelectrode connected to said last named conductor and having an effectivearea so small as to permit substantial current to flow only in onedirection, whereby said conical electrode is made to iunctionas acathode during the flow of said current, said conical electrode beingarranged so that the discharge takes place on the inside surface of thecone, whereby the discharge is permitted to select the optimum electrodediameter for ordinary variations of gas pressure within the tube.

6. In a high voltage unidirectional luminous discharge tube, anelongated glass envelope, a-

lead-in conductor sealed in one end of said envelope with a vacuum-tightseal, an open-ended conical electrode connected to the said condoctor, asecond lead-in conductor sealed in the other end of said envelope with avacuum-tight seal, a second electrode connected to said last namedconductor and having an efiective area so small as to permit substantialcurrent to now only in one direction, whereby said conical electrode ismade to function as a cathode during the flow of said current, and meansfor insulating said second named electrode and leadin conductor towithstand a high peak reverse voltage drop during reverse current in thetube, said conical electrode being arranged so that the discharge takesplace on the inside surface of the cone, whereby the discharge ispermitted to select the optimum electrode diameter for ordinaryvariations of gas pressure within the tube.

' MILES PENNYBACKER.

